Silencer with toroidal expansion chambers



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May 22, 1951 J. F. JOHNSTON SI-LENCER WITH TOIEOIDAL EXPANSION CHAMBERSFiled March 31, 1949 Patented May 22, 1951 .SILENCER WITH TOROIDALEXPANSION ERS CHAMB J. FordJohnstonQHampton, Va., assignor of onevhalfto John R. Anthony, Jr., Takoma Park, Md.

vApplication March 31, 1949, Serial No. 84,573

Claims. 1

This invention relates-to a silencer or muliler for suppressing .thenoise caused by the sudden exit of gas from or entrance of gas into areciprocating pump, compressor, engine or other device which maytransmit or otherwise handle gas With periodic pulsations.

Mufflers of conventional design employ charnbers equipped With bailles,slots, holes, and like devices for creating turbulence in the flow ofgas, all of which convert the kinetic energy of the gas into heat energywhich results in an increased back Ipressure at the exhaust valve or adecreased induction pressure at the inlet valve The .primary object ofthis invention is to suppress the noise attendant upon pulsating flow ofvgas by providing suitable chambers for transforming the pulsations intorelatively continuous viiow Withoutconverting kinetic energy into heatenergy. This may be achieved by the application of commonly knownaerodynamic and acoustic principles relating-to the handling of flowinggases.

The secondary object is to produce such a mui-- Viler havingphysicalcharacteristics which render it readilyadaptable to'loW-cost,high-volume production, and which will .be comparatively much smaller,in size than muillers of known construcber tothe other, the peripheralchamber being so shaped as to maintain a smooth now of gas. It'is aWell-known principle of acoustics that a sudden reduction of area ina'gas conductor will materiallyreduce the intensity of noise transmittedalong the conductor, but past designs using thisprinciple have alwaysfailed to maintain the kinetic yenergy of the gas, so that a highpressure differential rWas required to maintain the gas oW.

Thelvelocityvof exhaust gas leaving a valve port at beginning of'exhaust is supersonic. The function of-a muffler -is to ysuppress thenoise of the V.supersonic Wave front by reducing its velocity as much aspossible. inthe silencer of the present invention, ythe gas expands asVit leaves the inlet pipe, and the expansion causes the conversion ofpressure energy into velocity energy With the gas rotating at a highvelocity around the inlet. This rotation causes a partial vacuum atthe.center of rotation, due to centrifugal force. The creation of thepartial vacuum occurs after the supersonic Wave has passed, and ismaintained during the remainder oi the exhaust stroke. Therefore, sincethe exhaust strokeis completed during a time when the pressure is low,the weight of exhaust gas remaining in the cylinder from one cycle tothe next is minimized. In essence, the energy of the initial supersonicblast is utilized to provide a ylow pressure chamber into which thescavenging operation can discharge during the end of the stroke, whichisthe most important part of the stroke.

It will be obvious, of course, that the same design is effective as anintake silencer.

The invention is illustrated in the form of a two-piece casting, withparts riveted together. Using all the above-mentioned principles, thesilencer takes in the gas at its center, lets the gas escape into thecentral expansion chamber through diffuser vanes which impart to the gasa whirling motion about the axis of the inlet pipe, and then permits thegas to escape into a peripheral collection chamber through a peripheralslot. While the pressure Waves causing objectionable noise will spreadto the Walls of the central chamn ber, only a small portion of them willescape through the slot into the peripheral collection chamber. Thecollection chamber preferably is designed so that its cross section areaat any point is proportional to the position of the point vbetween thebeginning and end of the peripheral slot, in order to achieve themaximum smoothness of iloW.

The small part of the pressure wave which escapes from the centralexpansion chamber through the 4peripheral slot Will enter all parts ofthe peripheral collection chamber at approximately the same time.Therefore, the Wave front Will not be concentrated at one point in thecollection chamber, and its exit will be spread over the time requiredfor sound to travel the circumferential length of the collectionchamber. Most of the energy of the pressure waves will be absorbed bythe walls of the two chambers as they are reflected from side to side.

The pulsations in pressure of the incoming gas are smoothed out by theiactthat the gas in any given pulsation enters the central chamberwithout striking against any baille, but makes a gentle transitionalcurve in vchanging its direction, so

that a new pulsation meets no resistance except the gas in the centralchamber, which is already whirling rapidly in the same direction as thenew pulsation.

It has been found through experimentation that the peripheral slot area,for best performance, will generally be approximately one-twentieth toone-thirtieth of a square inch per brake horsepower of the engine.

The invention as illustrated in the drawings takes the form of a mufflerand is shown, generally, in a two-part casting.

In the drawings, Figure 1 is a top plan view of the assembled muiiier;

Figure 2 is a sectional View tak-en on the line 2--2 of Figure 3;

Figure 3 is a side view of the assembled muffler wherein certainportions of the inner construction are illustrated in dotted lines;while Figure 4 is a sectional view taken on the line 4-4 of Figure 1.

The upper casting is indicated generally by reference numeral A, whilethe lower casting is indicated generally by reference numeral B. Theupper casting A is provided with an annular extension I6 having ascrew-threaded bore II formed therein, for attachment to the manifoldpipe of an internal combustion engine or the like, wherein the pulsatinggases to be muffled originate. The upper casting A is in the generalform of a hemisphere, as indicated by reference numeral I2, while theouter periphery of the sphere is generally arcuately shaped, asindicated at i3, and an annular flange I4 is provided for attachmentthrough suitable bolts I to the lower casting B. A substantially annularpipe I5 is formed integrally with the casting A, the pipe IE having aplurality of angularly positioned diffuser vanes I1 formed therein.

The lower casting B, as illustrated particularly in Figures 2 and 4, isformed in substantially the shape of a hemisphere 20 and has a generallyarcuately shaped outer periphery 2| with a flange 22 formed thereabout,the ange 22 cooperating with the flange I4 of the casting A, and boltsI5 extending through the two flanges to secure the two castingstogether. An annular pipe 24 extends upwardly from the bottom of castingB, the pipe 24 being so positioned to register with pipe I6 so as toform a continuation thereof, pipes I5 and 24 being positionedsubstantially centrally of the castings A and B. Pipe 24 is alsoprovided with a plurality of angularly positioned diffuser vanes 25 soas to form a continuous slot with the vanes I'I formed in pipe I6. Whenthe two castings are assembled through their flanges I4 and 22, as shownparticularly in Figs. 3 and 4, the hemispheres I2 and 2G form asubstantially spherical inner chamber 3B. While this chamber 3i) hasbeen generally indicated as being spherical, it will, of course, beunderstood that it need not necessarily take the same shape as a sphere,although the same should be substantially toroidal. The arcuateextensions I3 and 2| form a substantially annular collection chamber 32,when Viewed in cross section, the collection chamber 32 taking the formof a spiral, as indicated in the drawings, the area of chamber 32gradually increasing from the point indicated at X as Zero to the outletopening 33.

The castings A and B are so shaped, at a point intermediate theexpansion and collection chambers, as to provide a peripheral restrictedslot 35 when the castings are positioned together, as seen particularlyin Fig. 4 in order to act upon the gases passing therethrough in amanner similar to a venturi. As the castings are subjected to certainheat and pressure, it is possible that the same may in time warp and,accordingly, suitable spacer elements 36 are positioned about theperipheral slot 35 so as to prevent the castings from closing whichwould in turn close the Venturi slot.

The bottom central portion of casting B is provided with a cone-shapedindentation 4D for purposes later to be described.

In operation, the assembled unit as illustrated in Figs. 3 and 4 issecured at the opening I I to the source of pulsating gases. The gasesenter the pipes IE and 24 and through the aid of the cone 4U andangularly positioned diffuser vanes II and 25 pass into the expansionchamber 30 in a whirlingl motion. The gases will continue their whirlingmotion and hence be thrown outwardly within the expansion chamber 30 andpass through the peripheral slot 35 into the collection chamber 32which, as has been noted, is generally in the shape of a spiral andgradually spreads from zero, as indicated at point X, to full area atthe outlet port 33.

As before indicated, the incoming pulsating gases expand in theexpansion chamber, which expansion causes the conversion of pressureenergy into velocity energy and the expanding gases rotate at highvelocity within the expansion chamber. A partial vacuum is therebyformed in the central portion of the expansion chamber, the partialvacuum occurring after the supersonic wave has passed. As the exhauststroke of the engine is completed during the formation of this partialvacuum, the weight of exhaust gases remaining in the cylinder from onecycle to the next is materially decreased. While the pressure waves,which cause the objectionable noises, will spread to the walls of theexpansion chamber, only a small portion of the pressure waves willescape through the peripheral slot into the peripheral collectionchamber. The small percentage of the pressure waves which thus escapefrom the expansion chamber into the spiral collection chamber willescape at approximately the same time and, therefore, the wave frontwill not be concentrated in the collection chamber and its exit will bespread over the time required for sound waves to travel thecircumferential length of the collection chamber. Also, most of theenergy of the pressure waves will be absorbed by the walls of the twochambers as they are reflected from side to side.

While the invention has been illustrated in the form of castings, itwill be obvious that the same may be formed of sheet metal or the likeand the various elements riveted or otherwise secured together. Also,the whirling motion may be imparted by other means than diffuser vanes.Sufcient whirl can be imparted to the gas in planes parallel to theinlet axis by placing a tall cone in the path of the incoming gas, whichgently turns the gas from its linear flow path without reflecting anappreciable pressure rise to the inlet pipe.

I claim:

1. A silencer comprising a hollow substantially toroidal expansionchamber, an inlet therefor, a collection chamber positioned about theouter periphery of said expansion chamber for receiving gases from saidexpansion chamber, a peripheral slot formed between said chambers toprovide communication therebetween, and an outlet for said collectionchamber, said collection chamber being formed by a substantially annularinner wall portion and a spiral outer wall portion whereby saidcollection chamber gradually increases in cross-section fromsubstantially zero to substantially the cross-sectional area of saidoutlet.

2. A silencer -comprising a hollow substantially toroidal expansionchamber, an inlet therefor, means for imparting whirlingI motion to theinlet gas in said expansion chamber, a collection chamber positionedabout the outer periphery of said expansion chamber for receiving gasesfrom said expansion chamber, a peripheral slot formed between saidchambers to provide communication therebetween, and an outlet for saidcollection chamber, said collection chamber being formed by asubstantially annular inner wall portion and a spiral outer wall portionwhereby said collection chamber gradually increases in crosssection fromsubstantially zero to substantially the cross-sectional area of saidoutlet.

3. An exhaust gas muler for internal com bustion engines comprising ahollow substantially toroidal expansion chamber, an exhaust gas inletconduit connected to said chamber, a substantially annular collectionchamber positioned on the outer periphery of said expansion chamber andhaving a gas outlet, a substantially continuous annular slot formedbetween said expansion chamber and said collection chamber providingcommunication therebetween, said slot being less than 360, and an outletfor said collection chamber, said collection chamber being formed by asubstantially annular inner wall portion and a spiral outer wall portionwhereby said collection chamber gradually increases in cross-sectionfrom subtantially zero to substantially the crosssectional area of saidoutlet.

4. An exhaust gas muiiler for internal combustion engines comprising ahollow substantially toroidal expansion chamber, an exhaust gas inletconduit connected to said chamber and extending therein, said inletconduit having diffuser vanes therein to cause the gases to rotatewithin said chamber, a substantially annular collection chamberpositioned on the outer periphery of said expansion chamber and having agas outlet, said collection chamber being formed by a substantiallyannular inner wall portion and a spiral outer` wall portion whereby saidcollection chamber gradually increases in cross-section fromsubstantially zero to substantially the cross-sectional area of saidoutlet, a substantially continuous annular slot formed between saidexpansion chamber and said collection chamber` providing communicationtherebetween, said slot being less than 360.

5. An exhaust gas muiller for internal combustion engines comprising ahollow substantially toroidal expansion chamber, an exhaust gas inletconduit connected to said chamber, a cone in said expansion chamber forcausing the gases to rotate within said chamber, a substantially annularcollection chamber positioned on the outer periphery of said expansionchamber and having a gas outlet, said collection chamber being formed bya substantially annular inner wall portion and a spiral outer wallportion whereby said collection chamber gradually increases incross-section from substantially zero to substantially thecrosssectional area of said outlet, a substantially continuous annularslot formed between said expansion chamber and said collection chamberproviding communication therebetween, said slot being less than 360,

J. FORD JOHNSTON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number

